1. Field of the Invention
The present invention relates to a gas generant composition. More specifically, the present invention relates to gas generant composition which is suitable to a gas generator for a human body-protecting bag for protecting car passengers from an impact in a collision or a sudden stop of traffic facilities such as automobiles.
2. Description of the Related Art
In recent years, an air bag system in which a bag expands by detecting a collision in order to prevent passengers from being killed or injured by colliding against a handle part and glass is rapidly increasing in a demand therefor in the midst of further growing requirement of safety to automobiles.
In the air bag system, after detecting an impact, an igniting agent is ignited in an instant by electrical or mechanical means, and a gas generant is ignited by this flame and combusted to generate gas, whereby a bag is expanded. It is essential for such the gas generant to have a low impact ignitability and a high combustion speed. The impact ignitability means an ignition sensitivity to an impact, and if this is too sharp, an explosion risk increases, which is not preferred in terms of safety. Accordingly, the lower impact ignitability is preferred. On the other hand, the low combustion speed does not expand a bag in an instant and therefore is not useful for the air bag. A minute time of 20 to 30 milliseconds is required to the time consumed during a collision through completing the expansion of the bag. In order to meet the above requirement, the combustion goes on preferably at a speed of 40 mm/second when the combustion speed is measured under a pressure of 70 kg/cm.sup.2. Further, with respect to the gas generant, resulting gas has to be harmless to human bodies, and a gas generating amount per unit weight has to be large.
The requirements described above lead to using mainly as a gas generant brought into actual use at present, substances containing, as a main component, metal azides such as sodium azide (NaN.sub.3) generating nitrogen gas.
The gas generant composition described in U.S. Pat. No. 4,931,111 improves in the self-retainability of a solid residue by adding clay but has the defect that a large amount of clay is required in order to obtain a sufficient effect, which brings about a marked reduction in the combustion speed and a deterioration in the ignitability. The gas generant composition described in U.S. Pat. No. 4,696,705 enhances a scavenging effect of a solid residue by adding a graphite fiber and tries to improve a combustion speed. That requires a fiber length of 1 mm or more, which provides the defect that processability is notably reduced and a graphite fiber is very expensive.
Further, as can be seen in U.S. Pat. No. 4,376,002, and U.S. Pat. No. 5,143,567, SiO.sub.2, TiO.sub.2, Al.sub.2 O.sub.3, and the like have been being used as slag-forming agents from the past. However, while all of them increase the viscosity of a residue and improve a scavenging performance by filters to some extent, they cause a great part of the residue to remain in a combustion chamber in the form of slug, and therefore lighter filters have not yet come to be possible. Further, the fixed amount or more has to be added in order to obtain an effect as the slug-forming agent, and in such case, a marked reduction in the combustion speed and the deterioration in an ignitability are brought about.
In view of the preceding problems on the prior arts, the subject to be solved by the present invention is to provide a gas generant composition which improves in the self-retainability of a solid residue and has an excellent combustion speed.